Powertrain systems include internal combustion engines that mechanically couple to transmission devices to generate, multiply and transfer torque to an output member. Transmissions may include selectively activated friction clutch packs that are hydraulically actuated. Hydraulic pumps may provide pressurized hydraulic fluid to transmission devices to activate and deactivate friction clutch packs. The engine may be capable of executing autostop and autostart events to discontinue engine operation during ongoing powertrain operation to conserve fuel. Hydraulic pumps that are mechanically driven by the engine stop spinning and thus no longer generate hydraulic pressure when the engine is shut down in response to an autostop event. It is known to use an electrically-driven auxiliary hydraulic pump to provide hydraulic pressure for clutch activation when an engine is shut down in response to an autostop event. An electrically-driven auxiliary hydraulic pump adds weight, consumes electrical power, requires packaging space, and increases system complexity of a powertrain system.